Outer Diameter Of Nanotubes Research Articles

EFFECT OF ANODIZING VOLTAGE ON THE PHOTOCATALYTIC ACTIVITY OF FILMS FORMED BY TITANIUM DIOXIDE NANOTUBES

The influence of the anodizing voltage during synthesis on the specific surface area and on the photocatalytic activity of the TiO2 nanotube was studied. Films formed by titanium dioxide nanotubes were obtained on the surface of titanium foil by electrochemical anodizing. It has been found that an increase in the anodizing voltage from 20 V to 60 V leads to an increase in the inner and outer diameters of nanotubes, an increase in the growth rate and the interpore distance of nanotubes. The photocatalytic activity of the samples was evaluated by measuring the magnitude of the photoinduced current. The film produced at low voltage generated a current 3.5 times higher than the film produced at high voltage, and the degradation of the dye in the presence of the films was 75 and 38%, respectively, over the same period of time. An increase in the photocatalytic activity of the films is mainly associated with an increase in the specific surface area of the nanotubes. Thus, the values of the specific surface area of TiO2 nanotubes were determined by the method of low-temperature nitrogen adsorption. It has been established that with an increase in the anodizing voltage, the specific surface area of the films decreases.

Function Calculation: A Simple Way to Predict the Geometry Parameters of Self‐Organized Titania Nanotube Arrays

AbstractTNTAs were grown by anodization of titanium in mixed electrolytes consisting of water, ethylene‐glycol and NH4F. With this electrolyte composition, the obtained nanotube layers show a high level of flexibility towards controllable tube geometries. We carefully investigated the internal relationship between the synthesis parameters and the resulting TNTA morphology, deriving a set of relations to link the preparation parameters with the geometric dimensions of the obtained TNTAs. We show that the nanotube outer diameter not only increases linearly with the applied anodization voltage, but also relates to the water content in the electrolyte, and that both the water content and fluoride content determines the kinetics of the tube growth. Thus, by adjusting the electrolyte composition and optimizing the anodization procedure, a wide range of pre‐defined morphologies can be realized.

Quantifying the transverse deformability of double-walled carbon and boron nitride nanotubes using an ultrathin nanomembrane covering scheme

We investigate the characterization of the transverse deformability of double-walled carbon and boron-nitride nanotubes (i.e., DWCNTs and DWBNNTs) using an ultrathin nanomembrane covering scheme. Monolayer graphene oxide sheets (MGOSs) with a sub-nm thickness are used to cover individual double-walled nanotubes on flat substrates. Nanotube cross-section height reduction occurs due to the compression force exerted by the covering membrane, whose morphological conformation is governed by its bending/stretching rigidities and adhesion interaction with the substrate, as well as the radial height and rigidity of the underlying nanotube. The actual transverse deformation of the underlying tube and its effective radial modulus are quantified through interpreting the measured structural morphology of the covering membrane and the nanotube cross-section height reduction using nonlinear structural mechanics and Hertzian contact mechanics theories. The radial deformations in MGOS-covered tubes are found to positively correlate with the nanotube radial rigidity, thus, increasing with the nanotube outer diameter and decreasing with an increase of the number of tube walls. Our results reveal prominent radial strains of about 20% for DWCNTs of 3.55 nm in outer diameter, while about 24% for DWBNNTs of 3.85 nm in outer diameter. Our data about the effective radial moduli of individual DWCNTs and DWBNNTs are in reasonably good agreement with those obtained using atomic force microscopy-based compression methods. Our work shows that the nanomembrane covering scheme is promising as a quantitative technique for studying the radial rigidity of individual tubular nanostructures.

Anodic TiO2 nanotubes powder and its application in dye-sensitized solar cells

An increasing energy demand and environmental pollution create a pressing need for clean and sustainable energy solutions. TiO2 semiconductor material is expected to play an important role in helping solve the energy crisis through effective utilization of solar energy based on photovoltaic devices. Dye-sensitized solar cells (DSSCs) are potentially lower cost alternative to inorganic silicon-based photovoltaic cells. In this study, we report on the fabrication of DSSCs from anodic TiO2 nanotubes (NT) powder, produced by rapid breakdown potentiostatic anodization of Ti foil in 0.1 M HClO4 electrolyte, as photoanode. TiO2 NT powders with a typical NT outer diameter of approximately 40 nm, wall thickness of approximately 8–15 nm, and length of about 20–25 μm, have been synthesized. The counter electrode was made by electrodeposition of Pt from an aqueous solution of 5 mM H2PtCl6 onto fluorine-doped tin oxide (FTO) glass substrate. The above front-side illuminated DSSCs were compared with back-side illuminated DSSCs fabricated from anodic TiO2 NTs that were grown on the top of Ti foil as photoanode. The highest cell efficiency was 3.54% under 100 mW/cm2 light intensity (1 sun AM 1.5G light, Jsc = 14.3 mA/cm2, Voc = 0.544 V, FF = 0.455). To the best of our knowledge, this is the first report on the fabrication of DSSC from anodic TiO2 NTs powder. The TiO2/FTO photoanodes were characterized by FE-SEM, XRD, and UV–Visible spectroscopy. The catalytic properties of Pt/FTO counter electrodes have been examined by cyclic voltammetry.

Rapid breakdown anodization technique for the synthesis of high aspect ratio and high surface area anatase TiO 2 nanotube powders

Clusters of high aspect ratio, high surface area anatase-TiO 2 nanotubes with a typical nanotube outer diameter of about 18 nm, wall thickness of approximately 5 nm and length of 5–10 μm were synthesized, in powder form, by breakdown anodization of Ti foils in 0.1 M perchloric acid, at 10 V (299 K) and 20 V (∼275 and 299 K). The surface area, morphology, structure and band gap were determined from Brunauer Emmet Teller method, field emmission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, photoluminescence and diffuse reflectance spectroscopic studies. The tubular morphology and anatase phase were found to be stable up to 773 K and above 773 K anatase phase gradually transformed to rutile phase with disintegration of tubular morphology. At 973 K, complete transformation to rutile phase and disintegration of tubular morphology were observed. The band gap of the as prepared and the annealed samples varied from 3.07 to 2.95 eV with increase in annealing temperature as inferred from photoluminescence and diffuse reflectance studies.

A Novel Method for Synthesis of Titania Nanotube Powders using Rapid Breakdown Anodization

The present paper describes a new method utilizing rapid anodization to quickly synthesize high-quality, high aspect ratio, robust titanium dioxide nanotube powders. TiO2 nanotube powders, with a typical nanotube outer diameter of approximately 40 nm, wall thickness of approximately 8−15 nm, and length of about 10−35 μm, were synthesized by potentiostatic rapid breakdown anodization of titanium foils in aqueous electrolytes of 0.3 M NaCl or 0.1 M HClO4 under an applied potential of 20 V. High reactivity and ultrahigh reaction rate are cornerstones responsible for periodic release of TiO2 nanotubes into solution and formation of a white precipitate of TiO2 nanotubes. The reaction yield is approximately 4−6 g in less than 3 h, and the approximate cost of the material is $3.50/g, based on the laboratory-scale production. Various characterization techniques, including FESEM, HRTEM, EDX, XRD, XPS, FT-IR, UV−visible diffuse-reflectance, and N2 adsorption, have been used to probe morphology, microstructure, crys...

Control of morphology and composition of self-organized zirconium titanate nanotubes formed in (NH 4) 2SO 4/NH 4F electrolytes

We investigated the formation of self-organized zirconium titanate nanotubes by anodizing a Ti-35Zr alloy in 1 M (NH 4) 2SO 4 + 0.1–2.0 wt.% NH 4F electrolytes. The morphology and composition of the zirconium titanate nanotube are controlled by the applied electrochemical conditions. The outer diameter of nanotubes is controlled by the anodization potential in the range between 1 and 100 V (versus Ag/AgCl). Tubes with diameters from 14 to 470 nm can be grown. The nanotube length correlates with the anodic charge up to a length where significant dissolution of the nanotube layer is observed. The wall thickness, composition of the nanotubes and porosity of the nanotube layer are significantly affected by the fluoride ion concentration. The length limiting factor of the nanotube growth is found to be the diffusion of ionic species in the electrolyte.

Synthesis and magnetic properties of Ni nanocylinders in self-aligned and randomlydisordered grown titania nanotubes

A novel ferromagnetic/semiconductor oxide nanocomposite formed by arrays of Ninanocylinders grown by the electrodeposition technique in a semiconductor oxide matrix ofself-aligned and randomly disordered titanium dioxide nanotubes has been synthesized.X-ray diffraction, EDX, SEM, AFM, rf-GDOES and VSM magnetometry techniqueshave been used to investigate the structural, compositional and morphologicalproperties, as well as its specific magnetic behaviour. Titania nanotubes have beengrown through a single anodization process, by using HF acidic electrolytes in apotentiostatic mode. The thus-obtained titanium dioxide nanotube outer diameter rangesbetween 90 and 150 nm, wall thickness about 25–40 nm and 300 nm in depth. Theelectrodeposited Ni nanocylinders reach above 100 nm diameter and 240 nm length,giving rise to coercive fields of 98 and 200 Oe, well within the hysteresis loopsperpendicular or parallel to the nanocylinder axis, respectively, which could beascribed to the formation of magnetic vortex domain states. It is expected that thisnovelty nanocomposite, based on ferromagnetic Ni nanocylinders embedded in asemiconductor titanium dioxide nanotube template, will become a promising candidate formany applications in a broad range of scientific and technological areas, suchas ultrahigh density magnetic storage media or spin-based electronic devices.

Magnetic behaviour of arrays of Ni nanowires by electrodeposition into self-aligned titania nanotubes

Arrays of Ni nanowires electrodeposited into self-aligned and randomly disordered titania nanotube arrays grown by anodization process are investigated by X-ray diffraction, SEM, rf-GDOES and VSM magnetometry. The titania nanotube outer diameter is about 160 nm, wall thickness ranging from 60 to 70 nm and 300 nm in depth. The so-obtained Ni nanowires reach above 100 nm diameter and 240 nm length, giving rise to coercive fields of 98 and 200 Oe in the perpendicular or parallel to the nanowires axis hysteresis loops, respectively. The formation of magnetic vortex domain states is also discussed.

Fabrication of a Carbon Nanotube-Embedded Silicon Nitride Membrane for Studies of Nanometer-Scale Mass Transport

Membranes consisting of multiwall carbon nanotubes embedded in a silicon nitride matrix were fabricated for fluid mechanics studies on the nanometer scale. Characterization by tracer diffusion and scanning electron microscopy suggests that the membrane is free of large voids. An upper limit to the diffusive flux of D2O of 2.4 × 10-8 mol/m2 s was determined, indicating extremely slow transport through the membranes. By contrast, hydrodynamic calculations of water flow across a nanotube membrane of similar specifications predict a much higher molar flux of 1.91 mol/m2 s, suggesting that the nanotubes used in the membrane have a “bamboo” morphology. The carbon nanotube membranes were then used to make nanoporous silicon nitride membranes, which were fabricated by sacrificial removal of the carbon. Nitrogen flow measurements on these structures give a membrane permeance of 4.7 × 10-4 mol/m2 s Pa at a pore density of 4 × 1010 cm-2. Using a Knudsen diffusion model, the average pore size of this membrane is estimated to be 66 nm, which agrees well with TEM observations of the multiwall carbon nanotube outer diameter. These membranes are a robust platform for the study of confined molecular transport, with applications in separations and chemical sensing.

Synthesis of Eu2O3 nanotube arrays through a facile sol-gel template approach.

Eu2O3 nanotubes have been successfully fabricated by an improved sol-gel template method within the nanochannels of porous anodic alumina templates. The morphology, structure, and composition of the nanotubes were characterized by means of X-ray diffraction techniques, scanning electron microscope, transmission electron microscopy, and selected-area electron diffraction. The results show that the Eu2O3 nanotubes are polycrystalline with a cubic structure. The outer diameter of nanotubes is 50-80 nm, and the thickness of the tube wall is about 5 nm. The mechanism of nanotube formation was discussed.

Control of the outer diameter of thin carbon nanotubes synthesized by catalytic decomposition of hydrocarbons

Multi-wall carbon nanotubes have been produced by the catalytic decomposition of acetylene. Co–Mo, Co–V and Co–Fe mixtures supported either on zeolite or corundum alumina were used as catalysts. When Fe or V is added to Co, the carbon deposit increases. The nanotubes were characterized by both low and high resolution TEM. From histograms representing the outer diameter distributions, it is clear that the outer diameter of the nanotubes can be controlled by choosing the appropriate catalyst.